The present disclosure relates to image reading apparatuses and image forming apparatuses that include the image reading apparatuses.
In general, an image reading apparatus includes an image sensor such as a CIS (Contact Image Sensor), and an AFE (Analog Front End).
The image sensor senses a light amount of reflected light, for each line in the main scanning direction, from a document that is moved relative to the image sensor, and sequentially outputs an analog image signal corresponding to the one line in the main scanning direction. The AFE is a circuit in which the signal outputted by the image sensor is subjected to a predetermined signal process. The AFE includes an offset adjustment portion and an amplifier portion.
The offset adjustment portion subjects the analog image signal to offset adjustment. The amplifier portion amplifies the signal having been subjected to the offset adjustment. By the offset adjustment, even if a reference level of an image signal outputted by the image sensor fluctuates, a signal obtained by removing, from the image signal, an offset component that includes an amount of fluctuation of the reference level, is amplified by the amplifier portion.